Filter presses are well known and extensively utilized for separating solids from slurries. Such filter presses employ a plurality of filter plates which are held in contacting relationship between a fixed and a movable head member while the slurry is pumped into and through the press for collecting the solids in the form of cake between adjacent filter plates. When the press is full of solids, the movable head is backed away from the plates into an open position and the plates are moved into an open position to permit discharge of the cake which is collected between adjacent pairs of plates. To permit movement of the plates into an open position, plate shifting mechanisms are typically provided adjacent opposite sides of the press for permitting automatic or manual control over plate movement and cake discharge.
Various types of filter plates are utilized in filter presses, depending primarily upon the material to be filtered and the process requirements. For example, one type of plate is a cloth-type chamber plate which includes recessed surfaces on opposite sides of the plate, each of which serves to form a filter chamber with an adjacent plate when the plates are clamped together. A cloth filter covers each of these recessed surfaces, and is either mounted on the plate by a gasket or is draped between two adjacent plates. Thus, slurry is pumped into the filter chambers formed between the filter cloths of two adjacent plates, and the liquid from the slurry passes through the filter cloth and is discharged through filtrate ports in the plates. The solids are trapped in the filter chamber between the adjacent plates and form a cake.
Another type of filter plate which is utilized when process requirements call for production of a dried filter cake is a membrane or diaphragm-type squeeze plate. The construction of this type of plate is similar to the cloth-type chamber plate, but the drainage surfaces on the opposite faces of the plate are flexible diaphragms or membranes which define pressurizing chambers therebehind. A filter cloth covers the outer face of the diaphragm on each side of the plate and typically extends beyond the plate, i.e., the filter cloths are typically draped between the adjacent plates. In this case, slurry is pumped into the filter chambers formed between two neighboring plates and the liquid portion of the slurry passes through the filter cloths and is discharged through filtrate ports in the plates. After the filling cycle is complete and the filter chambers formed between adjacent plates are filled with solids, and before the press is opened, pressurized air or water is supplied to the pressurizing chamber located behind each diaphragm, causing the diaphragms to flex outwardly and exert mechanical pressure on the filter cake. This also effects limited heating of the filter cake which, in conjunction with a vacuum applied to the discharge side of the filter cloths, causes additional moisture to be removed from the filter cake. An example of this type of arrangement and process is disclosed in U.S. Pat. No. 5,558,773. A similar press and process is also sold by the assignee hereof under the designation “J-VAP”.
While filter presses employing membrane-type filter plates have provided improvement with respect to removal of liquid from the filter cake, nevertheless such membrane-type filter plates are of limited capability with respect to their ability to provide effective heating of the filter cake to assist in moisture removal by vaporization. It accordingly has been proposed to modify the filter press to include heating plates in conjunction with membrane-type filter plates. In such proposal, as illustrated by U.S. Pat. No. 6,387,282, a plurality of rigid metal heating plates are alternately interposed between the plurality of conventional membrane-type filter plates. Each heating plate is hence clamped between a pair of membrane-type plates when the filter press is closed, whereby each filter chamber is defined between the opposed faces of the adjacent membrane-type filter plate and the adjacent heating plate, and the size of the filtration chamber and hence the capacity thereof is defined principally by the recess formed in the membrane-type filter plate inasmuch as the opposed surface on the heating plate is typically flat. Since the heating plate is constructed of metal and has interior chambers and passages for accommodating a high-temperature heating fluid therein, such heating plate is effective in permitting transfer of significant quantities of heat energy through the metal face of the heating plate into the adjacent filter cake. Such arrangement hence does permit increased heating and accordingly more effective vaporization of the liquid in the filter cake, whereby more effective removal of liquid from the filter cake can be achieved.
With a filter press employing alternating metal heating plates of the type described above, however, the overall construction of the filter press, in order to maintain the same press capacity, increases significantly with respect to the structure and size thereof since the same number of membrane-type filter plates must be maintained, and at the same time a substantially similar number of heating plates are incorporated into the press, thereby significantly increasing the overall size (i.e., length) and also the space requirements and cost of the press.
Other examples of plate-type filter presses employing heating plates to provide more effective heating of filter cake within the press are illustrated by U.S. Pat. Nos. 4,999,118, 1,049,715, and PCT Publication WO 95/27550.
Another filter press employs both membrane filter plates and heating filter plates disposed in alternating fashion along the press, with the plates being constructed so as to maintain press capacity without requiring any significant increase in either the number of required plates or the overall size of the press, while permitting heat to be effectively transmitted into the filter cakes formed in the filtration chambers to effect vaporization thereof. At the same time the filter press permits more effective removal of liquid or vapor from the filter cake, such as during air blowing and vacuum-drawing cycles. This filter press is disclosed in U.S. Patent Publication 2006/0032805, the disclosure of which is incorporated by reference herein in its entirety.
The filter press enables the heating plates to be provided with metal heat transfer surfaces which define one side of each filtration chamber. The overall construction of the remainder of the heat plate employs a frame constructed principally of a non-metal material to permit forming of the heating plates in a more economical and more consistent manner similar to the construction of the membrane-type filter plates.
When a filter press is closed, a filtration chamber is defined by opposed recesses defined between each adjacent contacting pair of membrane and heating plates, whereby a membrane can effect squeezing of the filter cake in the chamber from one side thereof, and the heating surface on the opposed plate can effect heating of the filter cake from the opposite side thereof. Each of the membrane and heating plates has porting associated therewith which preferably communicates with upper and lower extremities of the filtration chamber, with the upper and lower ports in the membrane plate preferably being substantially diametrically opposite the respective lower and upper ports formed in the opposed heating plate. The diametrically opposed upper and lower ports formed in the membrane and heating plates permit air to be effectively blown into and through the filter cake, with the air passing both transversely across the width of the filter cake and longitudinally through the thickness thereof, to significantly assist in removing liquid or vapor from the filter cake. In addition, the lower ports formed in the opposed membrane and heating plates permit communication to be established with the lower extremity of the filtration chamber adjacent both sides of the filter cake so as to permit more effective drainage of liquid therefrom.
The heating plates are defined by frames constructed of a plastic material so as to have a construction similar to the plastic frames defining the membrane filter plates, and the heat transfer surfaces are preferably defined by thin metal plates, such as of stainless steel, which are fixed to opposite sides of the plastic frame and extend over substantially the entire bottom of the recesses formed in opposite sides thereof so as to provide a high-efficiency heat transfer surface which contacts the filter cake over substantially the entirety of one side of the filtration chamber. With this arrangement, the high-temperature heating fluid supplied to and through the interior of the heating plate permits more effective transfer of heat to the metal heating plate, particularly since the plastic frame of the heating plate has a much smaller heat transfer capability and exerts minimal impact as a heat sink relative to its effect on removal of heat energy from the heating fluid.
In the above arrangement, however, the heating plate does not allow the passage of liquid or vapor therethrough. Thus, the surface area of the filter cloth through which suction is drawn to remove liquid is generally limited to areas about the periphery of the heating plate.
An object of the invention is to provide a filter press with an improved temperature transfer filter plate assembly for enhancing the removal of liquid and vapor when forming a filter cake between a membrane filter plate assembly and a temperature transfer filter plate assembly.
The present invention results in improved removal of liquid from a filter cake by providing a plurality of apertures extending through a temperature transfer filter plate. The temperature transfer filter plate is formed by shaping the inner and outer walls in a wavy or undulating configuration. Holes or apertures in alignment on the inner and outer walls contact and open into each other and are sealed thereabout forming a temperature transfer plate chamber defined between the inner and outer walls. Thus, the temperature transfer plate chamber that allows heating or cooling fluid to pass therethrough has spaced apertures extending therethrough in a predetermined pattern. The fluid enters the plate chamber on one side near an edge thereof and passes within the chamber around the sealed apertures.
The temperature transfer filter plate is part of a temperature transfer filter plate assembly having a filter frame with a divider wall or web for receiving filter plates on opposing sides thereof. Collecting chambers are defined between the inner wall of each respective filter plate and the respective facing side of the divider wall.
The arrangement enables flow of liquid from a filter cake through a filter cloth and then through the spaced apertures of the temperature transfer filter plate and into the collecting chamber. Thus, dewatering at the surface of the metallic temperature transfer filter plate is provided. The liquid in the collecting chamber is removed therefrom through a flow path arrangement in the filter frame.
Other objects and purposes of the present invention will be apparent to persons familiar with constructions of this general type upon reading the following specification and inspecting the accompanying drawings.